(1) Field of the Invention
The invention relates to a method of copper stripping in the fabrication of integrated circuits, and more particularly, to a cheap and safe method of copper stripping using a novel chemical mixture in the manufacture of integrated circuits.
(2) Description of the Prior Art
In the manufacture of integrated circuits, copper stripping is required in a number of situations, for example, after electroplated copper deposition in a damascene process with complete selectivity to the barrier metal, or stripping of bulk copper from silicon wafers such as for rework. One method of removing copper has been to use nitric acid. This method has several drawbacks. High purity nitric acid is expensive. The corrosive nature of nitric acid renders the acid dangerous to operators and unsuitable for most cleaning equipment and creates a serious disposal problem. Finally, nitric acid oxidizes the surface of silicon and produces a thin oxide that hinders further removal of copper. It is desired to provide a safe, inexpensive method for removing copper.
U.S. Pat. No. 5,207,867 to Cordani teaches the use of an aqueous acid solution to be used after conventional copper stripping for the purpose of removing residual metal specie from the surface of an insulating layer. The solution includes a mineral acid, a fluoride ion, and an oxidizing agent such as hydrogen peroxide. U.S. Pat. No. 5,348,590 to Shigemura et al discloses a preflux to be formed only on copper and copper alloys. A chelating agent for reacting with copper ions is added to the preflux. The chelating agent may comprise aminocarboxylic acids such as ethylene diamene triacetic acid. U.S. Pat. No. 5,244,539 to McGrath et al teaches a solder-stripping aqueous solution that will not damage the underlying copper. The solution includes nitric acid, ferric ions, halide ions, and ammonium ions. U.S. Pat. No. 5,410,396 to Somers et al also discloses a solder-stripping solution that includes ammonium fluoride, hydrogen peroxide, acid, and an 8-hydroxyquinoline compound.
A principal object of the present invention is to provide an effective and very manufacturable method of copper stripping in the fabrication of integrated circuits.
Another object of the present invention is to provide an effective and very manufacturable method of copper stripping without attacking or damaging the barrier metal layer in the fabrication of integrated circuits.
Yet another object of the invention is to provide an inexpensive and safe copper removal method in the fabrication of integrated circuits.
Yet another object of the invention is to provide a novel copper stripping method which can be employed using wet cleaning equipment without corroding or destroying the equipment.
A further object is to provide a novel copper stripping method which can be employed to remove minute copper contamination from any equipment without corroding or destroying equipment parts.
A still further object is to provide a novel copper stripping method employing a chemical mixture comprising an ammonium salt, an amine, and water.
In accordance with the objects of this invention an inexpensive and safe copper removal method in the fabrication of integrated circuits is achieved. Copper is stripped or removed by a chemical mixture comprising an ammonium salt, an amine, and water. The rate of copper stripping can be controlled by the concentration of the ammonium salt component of the mixture.
Also in accordance with the objects of the invention, a novel chemical mixture for stripping copper is provided. The novel chemical mixture for removing or stripping copper comprises an ammonium salt, an amine, and water. For example, the novel chemical mixture may comprise ammonium fluoride, ethylenediamine, and water in a ratio of 1:1:1.